International Journal for Numerical and Analytical Methods in Geomechanics最新文献

Strongly anisotropic geomaterials, such as layered shales, have been observed to undergo fracture under compressive loading. This paper applies a phase-field fracture model to study this fracture process. While phase-field fracture models have several advantages—primarily that the fracture path is not predetermined but arises naturally from the evolution of a smooth non-singular damage field—they provide unphysical predictions when the stress state is complex and includes compression that can cause crack faces to contact.

Building on a recently developed phase-field model that accounts for compressive traction across the crack face, this paper extends the model to the setting of anisotropic fracture. The key features of the model include the following: (1) a homogenized anisotropic elastic response and strongly anisotropic model for the work to fracture; (2) an effective damage response that accounts consistently for compressive traction across the crack face, that is derived from the anisotropic elastic response; (3) a regularized crack normal field that overcomes the shortcomings of the isotropic setting, and enables the correct crack response, both across and transverse to the crack face.

To test the model, we first compare the predictions to phase-field fracture evolution calculations in a fully resolved layered specimen with spatial inhomogeneity, and show that it captures the overall patterns of crack growth. We then apply the model to previously reported experimental observations of fracture evolution in laboratory specimens of shales under compression with confinement, and find that it predicts well the observed crack patterns in a broad range of loading conditions. We further apply the model to predict the growth of wing cracks under compression and confinement. Prior approaches to simulate wing cracks have treated the initial cracks as an external boundary, which makes them difficult to apply to general settings. Here, the effective crack response model enables us to treat the initial crack simply as a nonsingular damaged zone within the computational domain, thereby allowing for easy and general computations.

This paper presents a series of laboratory free-fall cone penetrometer (FFCP) tests conducted on marine clay samples collected from the Gulf of Finland in the Baltic Sea. Subsequently, these tests are replicated numerically with the generalized interpolation material point method (GIMP) simulations. First, the paper gives laboratory-scale FFCP experiment results used for the validation of the numerical framework. In these experiments, a small-scale model of a FFCP was dropped from various heights into a natural marine clay soil sample and recorded using a high-speed camera. The tests were supplemented with a laboratory test program to determine the geotechnical properties of the clay used in the experiments. Following image processing, the tests provided data for numerical simulations: displacement, velocity, acceleration, and reaction force curves associated with the FFCP during the penetration process. The GIMP simulations shown in the paper replicate the process of penetration of the FFCP into the marine clay. The simulations used a strain-rate dependent Tresca constitutive model, extended with strain softening that replicates the reduction of the undrained shear strength due to destructuration, an important feature of the material. The numerical simulations replicate the experiments well. The study examines the effect of cone penetrometer roughness, impact velocity, mesh density, strain rate, and strain softening on the cone penetrometer penetration process. The simulation results indicate that the presented framework can replicate the dynamic penetration process on soft and sensitive clay very well.

Backward erosion piping (BEP) is a significant contributor to failures in global flood protection infrastructure, yet it remains among the least understood geotechnical phenomena, particularly concerning the fundamental mechanisms driving its initiation. This study focuses on the development of a novel stochastic framework for the prediction of critical hydraulic gradients causing BEP initiation. The novelty of the study lies in the following: (1) the development of a grain-scale probabilistic model based on fundamental mechanisms by means of the theory of rate processes, (2) quantification of the influence of soil variability on BEP initiation probability by introducing an initiation probability function, and (3) an analytical framework reconciling grain kinetics of BEP initiation with the Weibull distribution. A particle-scale BEP initiation probabilistic model is first established based on fundamental grain kinetics under seepage flow by using the theory of rate processes. To investigate how soil variability influences initiation, a stochastic dual random lattice modeling framework is exercised, complemented by direct x-ray computed tomography measurements of soil variability conducted on sand samples. The analytical probabilistic model for BEP initiation closely aligns with the Weibull distribution, also demonstrating that soil variability influences both the scale and shape parameters of the distribution. This work establishes the linkage between probability of BEP initiation as described by the theory of rate processes and phenomenological Weibull statistics. Findings presented herein bring the potential to develop a multiscale probabilistic framework by means of Weibull statistics for evaluating the probability of BEP initiation at multiple scales.

Backward erosion piping (BEP) is a leading internal erosion mechanism for flood protection system failures. A model capable of predicting critical hydraulic conditions for BEP initiation at multiple scales while also incorporating soil variability is a pressing need. This study formulates and validates a novel multiscale probabilistic BEP initiation framework with incorporation of soil variability. The framework is based on a grain-scale probabilistic model and the weakest link theory, and the theory of rate processes. The multiscale framework proposed herein is validated through a wide range of available experimental data from independent sources, encompassing tests performed at multiple scales. Following calibration with small-scale experimental data, the model demonstrates accurate prediction of critical hydraulic gradients at larger scales (3–6 orders of magnitude difference), including the ability to capture the grain size dependence of BEP initiation and providing uncertainty estimates. A systematic analysis is performed to uncover the effects of different soil properties on multiscale critical hydraulic conditions.